Electric conversion.



S. SABOT.

ELECTRIC CGNVERSION.

APPucATmN FILED AuG.22. i912.

Patented July 18, 1916.

4 SHEETS-SHEET l.

EESSEE:

Wm-N

S. CABOT.

ELECTRIC CONVERSION.

APPLICATION FILED Aumz, 1912.

Patented July 18, 1916.

4 SHEETS-SHEET 2 -mumdm S. CABOT.

ELECTRIC CONVERSION.

APPLICATION FILED AUG. 2 2. I9I2.

Patented my I8, 19m.

4 SHEETS-SHEET 3.

S. -CABOT. ELECTRIC CONVERSION. APPLicATIoN FILED Aue.22,1912.

Patented July 18, 1916.

4 SHEETS-SHEET 4.

SEWALL CABOT, F BROOKLINE, MASSACHUSETTS.

ELECTRIC CONVERSION.

Specification of Letters Patent. Patentd July 18, 1916 Appiicann ineaAugust 22, 1912. serial No. 716,359.

T0 all whom t may gonggrn; at another potential in accordance with theBe it known that. I, SEWALL CABoT, citiprinciple of my invention. Fig. 4is a front zen of the United States, and resident of elevation of amodification of the apparatus Brookline, in the county 0f Norfolk and Sl10WI1 111 Flg-l, from Which Certain details, State of Massachusetts,have invented il 118W lz, the C1'0SS-bl1'S 62 @n Mld their HSSO- unduseful huprnvelnent in Electric Conver-V ciated brushes andbrush-holders, as well as sion, of which the following is a specicathebIUSll-lloldtls 7h "l, @We 21nd their tion. brushes m1, m1', etc., havebeen omitted for My invention relates to the conversion of the Sake ofclearness. Fig. is a diagram polyphase current to direct,current andvice Showing one method of electrically connectversa and also totheConversion 0f direct ing the several parts which constitute the currentat one potential to direct current at Ughthitld POIlOIl of the apparatusillusanother potential, by polyphase commuta\ tmtel m Flga and Flg- 6,15a dmgl'm .on, Showing one method of electrically connect- The Object ofmy invention is t0 provide, u ing\t ie similar parts which constitutethe system of polyphase commutation wherein lethnd Pol'tlon 0f SadaPlmmtug- Flg- 7 the necessity for shifting the angle of com- 1S il PMUShOWlllg Ono arrangement of mutation undelvnrying loads t0 preventbrushes an l-brnsh-liolders associated with undue sparking is obviated.the disk D1. F1g 8 1s a diagram of a com- I un tuuu-e tnut Systems 5fpnlyphuse p lete system snowrng\ one arrangementor` commutation areold,l but so far as I am adcircuits that may be empioyed in connectionvised they have never come into commerwith the apparatus shown in Figl 4for concial use because the necessityy for shifting Veltllg polyphasccurrent, -phase current the angle of commutation with changes of 111 thepresent instance. to direct current load to prevent sparking hasrendered them Mld "100 Yels- Figa 9 S il flfgn'lentl'y impracticable. Ihave discovered, however, Vlew showing 1n central longitudinal sectionthat if the transformer employed be de- Il POI `10I1 of 011e of thetransformer cores Signed tO have sufficiently Smu11-1enkage-inand itsassociated primary and secondary ductance, which, as herein explained,is the Wmdmgscoefiicient of magnetic-leakage, such necessity forshifting the brushes with varying more fully lllustratmg my mventon. Mloads is obviated, as vhereinafter vmore fully represents u l-poleSelf-Starting synchrosct forth. nous motor connected by the flexiblecou- In the drawings which accompany and pling B to the shaft H rotatingin the jourform a part of this specification I have illusnalS A1 A2.Mounted upon said journals trated several forms of apparatus and ararethe Supporting members D1 D2 herein rangements of circuits whereby theforegoshown as disks preferably of insulating maing objects may berealized. terial which are arranged to be adjusted In thedrawings,-Figure l is a front elcabout said journals and held inadjusted ration of one embodiment of my invention, position by the setscrews K1 K2, respec from which certain details, viz., the crosstively,thus constituting the equivalent of bars e2 e.rl and their associatedbrushes rocker arms. Collector rings C1 C2- are and brush-holders, havebeen omitted for mounted to rotate with the shaft H and are the sake ofclearne. Fig. 2 is a diagram insulated therefrom. Brush-holders I1 I2,showing one arrangement of circuits that supported on the disks Dl DE.,respectively, may be employed in' connection with the apcarry brushes J1J2 which 'make contact paratus shown in Fig. l for converting polywiththe collector rings C1 C2 respectively phase alternating current,S-phase current and constitute the DC terminals of the apin thisparticular` instance, into direct curparatus, said brushes and ringsforming a rent, or vice versa. Fig. Bis a diagram of collecting device.The shaft H also carries a modification showing one arrangement of aninsulating disk C, in the periphery of circuits whereby direct currentat one powhich are set a plurality of contact segtential may beconverted into direct current ments S, S2A S3 S4, each shown inthe pres-In the particular drawings selected for 4 equally spaced around theperimeters thereof are a plurality of horizontal supports el e9. Inthepresent instance nine such supports are shown spaced forty degrees.apart from center-to center. The horizontal 'supports carrybrush-holders f1 fg, respectively, and brushes g, 1.- gf, are secured totheir respective brush-holders. The brushes g1 g, are connected to theti-phase. terminals 1 9 respectively of the transformer T adapted 'tochange polyphase current'of one system to polyphase current of anothersystem, and

herein shown-as a 3-phase, 'S9-phase trans-v former, having its S-phasewindings 10 11 12 "connected to the leads 10, 11, 12, 'respectively. Itwill be understood of course that while I have shown the windings 10 1112 in triangular connection, they may lbe employed in star connectionwithout departing from the principle of my invention. The transformer Tpreferably isa constant potential transformer having, in the presentinstance, three magnetic circuits around which are distributedin themanner hereinafter set forth, windings for changing symmetrical B-phasecurrents to symmetrical Q-phase currents. The -transformer T isdesigned, as hereinafter more fully de- -scribed, to have itsleakage-inductance or coefficient of magnetic-leakage suiiiciently smallto render unnecessary the shifting of the angle vof commutation withvarying loads to prevent sparking at the commutator C3.

The operation ofthe system above described is as follows: To transformconstant potential B-phase current to constant potential direct current,the motor M is started, a source of S-phase current is connected throughresistance to the terminals l0, 11, 12, land the disks D1 D2 adjustedabout the journals until the point of minimum sparking is reached. Theresistance may then be removed and a constant potential direct currentdrawn, from the brushes JQJ2 without the necessity for altering theadjustment of said disks in order toprevent sparking at the commutatorC., for varying loads up to the full rated output of the transformer.InV other words, by virtue of the small leakage-inductance of thetransformer the polyphase current may be sparklessly 'commutated for allloads within the rated output of said transformer with xed brushes or afixed angle of 'commutation To convert direct current to B-phasecurrent, the motor M (which is not necessarily a synchronous alternatingcurrent motor in this case) l bars e1 Y.

is started and the direct current source connected tothe brushes J1 J2.'Constant potential 3-phase current may then be drawn from the terminals10, 11,12, having a frequency numerically equal to twice the speed ofthe motor in revolutions per second. Here again, by virtue of the smallleakage'- inductance ofthe transformer the apparat'us will operatesparklessly for all loads within the rated output of the transformerwith a fixed angle of'comn'iutation. If it .is desired to transformdirect current of one potential to direct current of another potential,a second polyphase winding may be wound on the cores of the transformerT in place of the S-phase winding. This second polyphase winding is inall respects similar to that shown in Fig. 2 with the exception that theturns of its windings may be more, or less, numerous than those of thefirst tl-phase winding, the ratio of the turns of the two windingsdetermining the ratio of transformation desired.

In Fig. 3 the terminals of the second polyphase windinO, herein shown asa 9-phase winding, are shown at 1 9 and each is connected with one ofthe brushes g1 Q9 supported respectively by` the horizontal e9 of anapparatus identical withthat shown in Fig. 1. This apparatus comprisesbrushes Ji, J2 which make contact respectively with the collector ringsG1 02' and said collector rings are connected respectively with thesegments S1 SS and S2 S4 carried by the commutator C3. This apparatus iscarried by standards similar to those shown at A1 A, in Fig. 1 andpreferably is located on the other side of the motor M, the shaft H ofwhich carries the several collector rings C1 C2, C, C2 and thecommutator disks C3 C3". In the present inst-ance the second 9-phasewinding is shown as having more turns per winding than the first Q-phasewinding, so that when direct current of a givenpotential is suppliedtothe brushes Jl J2, a direct current of higher potential may be drawnfrom the brushes J1" J2.

I will now proceed to explain what I believe to be the principle ofoperation of the apparatus and system of circuits above described.

Polyphase alternating current having a small number of phases, suhforexample,

as S-phase current employed in the comare connected' in series in theusual well known manner. 'Iheir turns are so proportioned as to form asymmetrical a-phase system connected in polygon. The vectorial anglesand magnitudes of the fa-phases may then be represented by anequilateral polygon having n-sides. The voltage of each windingobviously will be zero twice per cycle and 4if two connections shiftingsynchronously with the terminalsv of said nphase windings are soadjusted that said windings are successively ',short-circuited each atthe instant in the cycle when its voltage is zero, a maximum fluctuatingunidirectional difference of potential will exist between saidconnections. For example, if as in the present case selected forillustration, n is taken as nine, the fiuctuationwill be 1.5 per cent.and the value of the direct currentvoltage will approximate four timesthe root-mcairstplare value of any one of the nine. phases. A directcurrent voltage which fluctuates only Loper cent. may be considered asunfluctuating for all practical purposes, and will cause apractically-um fluctuating direct current to flow in a Working circuit.Associated with the seconda-ry windings of the wphase transformer is theconnnutator C.z rotated by a synchronous motor M which is energized bythe same current that energizes the primary of said transformer. Thecommutator, together with its cooperating brushes, with which it hasrelative synchronous motion, thus provides the said synchronouslyshifting connections, whereby constant potentialpractically-untluctuating direct current may be obtained. Somewhatanalogous phenomena occur in the direct current dynamo in which thearmature windings form a symmetrical llt-phase vstem connected inpolygon and equipped vwith a. coinmutator and brushesv between whichexists relative synchronous motion. The brushes in this case. are soadjusted that each phase is commutated at the instant of zero potential.

Se far as I am aware, systems analogous to that described ove inconnection with l? l, 2 and 3, h e not been commercially ssfulr becausof a prohibitive amount of sparking at the commutator which occurredunless the bruslu* were adjusted for variations 1.1 load. l vediscovered that this difficulty resulted om the unsuitable design of thetransformers employed. I have found, however, that the problem is noteX- actly the same as in the direct current generator, because in thelatter the inductance between adjacent commutator segi'uents containsenergy stored by the load current, and this energy must be dissiliatedand re-stored while the winding .is short-circuited in order to securesparkless commutation. This inductance, causing reactance voltage, whichis the fundamental source of trouble, can be reduced only by increasingthe number of armature windings and commutator segments for a givenvoltage. However, in the case of the polyphase transformer, the fluxproduced by the load current in any of the secondary windings, is to acertain 'extent neutralized by the flu-X produced in the same place bythe action of the current in the pri mary or supply circuit.` Theresultant inductanceY I-have found to be the leakage linductance of thetransformer referred to one of the n-phase windings cemmutated.

y In the case of my polyphase transformer described herein the fluxproduced by the load current in any givenv place is to a very largeextent neutralized by the linx produced iny the same place by the actionof the current in the primary of the supply circuits The resultantinductance is the leakage-inductance of the transformer referred to oneof its a-phase windings and its magnitude in henries is determined bythe following equation in which nzthe number of turns in an n' phasewinding, pzthe mean perimeter of Adivided by the current. It has thesame .form as thev expression for the coefficient of self-induction,commonly called inductance, viz.,

where e is the flux, n'the number of turns, and I the current. Thefactor L,- which I term the leakage inductance, is the coefficient ofmagnetic leakage Ior;` leakage induction. This factor multiplied by thedirect current in an n-phase winding and divided by the time in secondsthat each phase is short-circuited by the shifting connections7 abovereferred to, gives the reactance voltage, and said voltage must beneutralized by an equal and opposite voltage in order to securesparkless commutation or reversal kof said current. Heretofre inpolyphase commutation systems, such voltage necessary to neutralize thereactance voltage.' was secured by shifting the angle of 130commutation. By means of the present invention, I am enabled to securesparkless commutation for all loads within the rated output of thetransformer without shifting the angle of commutation.

Ifit were possible to construct the transformer with an inappreciableleakage-inductance, it would be possible to handle loads even higherthan the rated output of the transformer without ever shifting the angleof commutation and furthermore, brushes of inappreciable resistancemight then be used, thus eliminating the element which has heretoforecaused the bulk of the losses in prior attempts to operate polyphasecommutation systems. lVhile it is probably impossible to construct atransformer havingsuch negligible leakage inductance, nevertheless Ihave "made and successfully operated in the system above described atransformer having sufficiently small leakage inductance to renderunnecessary the shifting of the angle of commutation to secure sparklesscommutation for all loads within the rated output of the transformer.The transformer which I prefer to employ differs from those now incomme' cial use in certain features whereby the leakage inductance isreduced to a minimum without decreasing its efficiency or rendering itsmanufacturing cost prohibitive. For a given rating this transformer hasa greater ratio of length to diameter of winding than the usualcommercial transformer and also has a larger ratio of iron to copper.The voltage per turn is greater than in the usual transformer and all ofthe inductivelyassociated primary and secondary windings on each coreare sandwiched or mutually interleaved to the g'. eatest possible extentso as to distribute them in as nearly even a manner as possiblethroughout the same position in space. To accomplish this result I use amaximum of iron, a maxinnun of voltage per turn, and a minimum ofcopper. I make the windings as long as feasible, and

I sandwich or mutually interleave the pri-' mary and secondary windingsin a manner well understood by those skilled in the art oftransformer-design, to the maximum extent feasible. The relativeproportion of all the inductively-associated windings in each unit areaof a central longitudinal section of a properly designed winding will bethe same, provided of course that such areas are each suiiiciently largeto include both pri-` mary and secondary turns. For example, if in agiven unit area in a certain part of said section, e' per cent. isoccupied by the primary winding, y/ .per cent. by polyphase winding No.l and .e per cent. by polyphase winding No. Q, etc.,-thcn in all otherdifferently located unit areas in said section, a? per cent. will beoccupied by the primary turns, g/ per cent. by secondary winding No. 1and s per cent. by secondary winding No.

2, etc. This of course represents the ideal condition and my inventioncontemplates as close an approximation thereto as is possible. Thisinsures that the primary and secondary load fluxes shall be developed inthe same position in space, so that the one will neutralize the other ascompletely as possible, because, of Course the inducing and inducedcurrents are necessarily in opposite directions.

It is of course wellunderstood by those skilled in the art that magneticleakage in a transformer may be reduced by sandwiching the primary andsecondary windings. Heretofore in single phase transformers no occasionarose for reducing the leakage-reactance, (the product oflealnige-inductance by frequency) to more than about ten per cent. ofthe load resistance, for any further reduction obviously would beimmaterial since the leakage impedance varies according to the squareroot of the sum of the squares of the leakage-reactance andload-resistance. Therefore no material gain was secured in reducingmagnetic leakage beyond a certain minimum in single-phase alternatingcurrent transformers. The reason for the excessive reduction ofleakage-inductance in my polyphase transformer is founded on mydiscovery that the difficulty in securing polyphase commutation may bedecreased proportionately to the reduction of leakage-inductance. and onthe further discovery that sparklcss commutation with a fixed angle ofcommutation for varying loads is possible when the leakage-inductance issufficiently small. Heretofore, in the proposed systems of polyphasecommutation of the prior art, no one has been ableto reduce thereactance voltage, which as above set forth is caused by the leakageinductancc, to less than 5:27 volts per phase, whereas in my system itis not larger than .75 volt per phase and the recognized permissiblemaximum is 2 volts when the angle of commutation is not automaticallyshifted. l

In the appended claims I use the term transformer having very smallleakageinductance7 as meaning a transformer hav- -ing a leakageinductance sufiieiently small that all loads within the rated output ofthe transformer can be handled without undue sparking and withoutshifting the angle of commutation. A

I have found the apparatus shown in the drawings especially suitable forrelatively high DC potentials, for the reason that the high potentialQ-phase terminals are separated by a considerable air-space at all timesexcept the instant when the potential difference is substantially zero.

I have constructed the apparatus shown in Figs. l. and :2 to transformQED-volt, GO- cycle. S-phase AC to 80,000-volt DC, which worked in asatisfactory manner for produclOJi mutation angle, forl all loads upcase, which, so farasgI am aware, is the first instance that as great apower as 16 K. W. has been attained with direct current at voltages ofthis magnitude. The dimensions of the a paratus were as follows: Thediameter of i2 was 18". The diameter of C, C2 was 14". The space betweenCl'or C2 and C2 .was 10". .The weight of iron in transformer T was 200lbs. The weight of copperin transformer T'was 30 lbs. The

volts per turn were three. The windings of transformer T consisted oftwo high potential sections X, X (Fig. 9)` sandwiched between three lowpotential sections Y, Y',

lf", on each core Z, each said high potential section containing thelayers of those secondaries that were wound on the core in question andeach said low potential section containing the layers of the primarywinding that surrounded said core. The length of eac-h core was about S,its diameter about 3 and the overall diameter of .cach core and windingwas about 6". As shown in Fig. 1, there was one primary foreach core,each primary having its entire length wound on one core, and, as shownin Figs. 1 and 2, each core had the whole of one secondary and portionsof four. others wound thereon, the diagram of the transformer in Fig. 2showing,'as is. customary,'the vector positions of the phases inquestion, as well as the connections of the windings. It will be notedthatin Fig.v 1 three conductors 1, 2 and 6 are shown as extending from.the windings associated with oneI core to connect the same with thebrushes ofthe commutator. As shown in Fig. 2, conductorl'yis connectedbetween secondaries IX and I..

conductor 2 between secondaries I and I I and conductor G betweensecondaries V and VI. Therefore it follows that the w 'le of secondary Iand parts .of secondaries X, II, V and VI are vwound on onecoreIteferiing to Fig. 1, conductors 4f, 5 and 9 eX- teiid from the windingson the second core, and by reference to Fig. 2 it will be seen thatconductor 4 is connected between secondaries III and IV, conductor 5between secondaries IV and V, and conductor y9 between secondaries VIIIand IX., Therefore it follows that the whole of secondary7 IV land partsof secondaries III, V, VIII and IX are wound on the second core.Conductors 7, S and 3 are shown in Fig. 1 as extending from the windings'associated with the third core, and by reference to Fig. 2 it will beseen that conductor 7 is connected between secondaries VII and VII,conductor 8 betwveen Secondillles and and con ondary VII and parts of-secondaries VI, VIII, II and III are wound on lthe third core.-

. Itis to be understood, of course, that my 'inventionis not limited t0the use of a phasechanging transformer 0f this type, for as will beobvious, `any other suitable transformer, `many typesA of which are wellknown, may be' employed. Whatever the type employed, it is essentialthat its leakage inductance be made very small as explained above, bydistributing all of 'the inductivelyassociated primary and secondarywindings on each corein as nearly even a-manner as possible throughoutthe same position in space, so that each integral portion of thesecondary winding is distributed in as nearly even a manner as possiblethroughout the same position in space surrounding its core as isoccupied by its inductively associated primary winding, incontradistinction, for example, -to a transformer for convertingtwo-phase current to twelve-phase current in which a primary coil isextended over both cores and the whole of a twelve-phase coil is Woundon only one core, the inductively vrelated primary and secondary coils,in such case, not being distributed evenly throughout the same positionin space surrounding the core and the leakage-inductance of thetransformer, consequently, being large.

I have found it possible to increase the f maximum load that can behandled without undue sparking and with a' fixed angle .of commutationby means of the above described apparatus modified as shown in Fig.

vision described and claimed in my United I States Letterslatent No.917,749, granted April 13, 1909. In Fig. el, four collector-rings C1 C1and C2 C2 are connected respectively to the segments S2 S3 and S2 S4 setinto the cominutator C3, as shown in Figs. 5 and G. Brushes J1 J1 arecarried by a suitable arm I1 on the disk D1 and brushes J 2 J2 arecarried by a similar arm I2 carried by the disk D2', or they may becarried on any of the horizontal supports shown in Figs. a, 5 and 6. Thebrushes .I1 J2 J2 J2 make contact respectively with the collector ringsCl C1 C2 C2', respectively, which are mounted on but insulated from theshaft H, which is driven as in Fig. 1 by a synchronous motor. The disksC4 C4 are of insulating material and each carries a plurality ofsegments r1 r2, r1 r2, respectively, herein shown as nine in number,each twenty degrees in circumferential ice leiigggth. Upon the edge ofthe disk C1t bear brushes ml m16 mounted respectively pair by pair oninsulating brush-holders n, m18, which are supported by the disk D1',and similar brushes m1 m16 mounted respectively pair by pair oninsulating brush-holders n, ns supported by the disk D2 bear upon theedge of the disk C4. The disks C, C4 are made wide enough, as shown inFig. 7, to allow the brushes to be mounted in pairs side by side withasmall gap betweenthem. These brushes obviously will be electricallyconnected when resting on a conducting segment r1, etc. or '11,', etc.,

and disconnected when resting on the edge of the disk itself.. Inthismanner a circuit .-.through four pairs of brushes is made and iWinding being commutated, a break7 E.M.F.

broken simultaneously at eight places in.`

series. At the instant of rotation shown in Fig. 5, thepolyphaseterminal l connected to brush g, is about to be connected tothe -i- DC terminal through S C, .Il m, 1', m2 Y m3 r1 m4 m5 r2 mb. fm,Tr3 'm8,' and polypliase terminal 9 connected to brush g, is about to bedisconnected fronigthe -l- DC terminal through S3 Cl J1 m10 rar/tw mi,r, m13' ml2 r6 mi, m10 1', m9. At the same moment,

in Fig. 6, polypliase terminal 5 connected to brush g5 is connected tothe DC terminal i through S2 C2 J2 m1 r9 m2 m3 r1 mi m5 'r2' me 'm7' r3m8. At this instant the Vpolyphase winding between terminals 9 and l isabout to be commutated, as shown in Fig. S. The next commutation tooccur will be that of the winding between the polypliase terminals 54and 6 and this is accomplished by a 10 clockwise rotation from the iposition shown. The result obtained by applying the principle of serialsubdivision in this manner is to cause an E. M. F. of relatively largeramount to be developed for a relatively short period of time. Thedirection of this E. M. F. issuch -as will reyversejthe flow of currentin the polypha'se opposing the. current creating it, so that when thestored energy to be commutated is relatively small, sparking does notoccur,

the necessary vdissipation of energy presumably taking place in the formof eddycurrents; but when `this energ is relatively large, sparking doesoccur at the points of The operation of the system shown in Fig. 8 isidentical with that above described in connection with Figs. l, 2 and 3,as will be obvious from comparison of Figs. 2 and 8.

It will be understood that various modifications m'ay be made both inthe apparatus and circuit connections herein shown and described withoutdeparting from the principle of my invention.

Iclaimz- 1. Anelectric conversion system comprising in combination, asource of polyphase current having a given number of phases, atransformer having a very small leakageinductance adapted to change saidcurrent to polyphase current .having a greater number of phases1 acommutator and a plurality of brushes associated there ith forsuccessively short-circuiting the secondaries ot said transformer, meansfor creating lrelative motion between said coinmutator and brushes insynchronisin with said current, a plurality of conductors connecting thesecondaries of said transformer with said brushes, and means for takingottthe resulting practically-uniuctuating direct current from saidcommutator.

2. An electric conversion system compris- -ing in combination, a sourceof polyphase current having a given number of phases,4 a

transformer having very small leakage-in- I.

ductance adapted to change said current to polyphase current having agreater number of phases', and means for converting said last-mentionedpolyphase current into p actically-uiifiuctuating direct current, saidmeans comprising apparatus for simultaneously connecting ordisconnecting at a plurality of points in series the direct currentcircuit to or from the secondaries of said transformer.

3. An electric conversion system comprising in combination, a source ofpolvpliase current of one system, a transformer having 'very smallleakage-iiiductance adapted to change said current to polyphase currentof a different system, a commutator, a plurality of brushes therefor,means for creating relative motion between said commutator and brushesin synchronisin with said cui'- rent, a plurality of conductorsconnecting the secondaries of said transformer with said brushes, andmeans for taking oli' thel resulting practically-unfluctuating directcurrentfrom said commutator, said means comprising apparatus forsimultaneously by converting said polyphase current intopractically-unluctuating direct current, 'and means for adjusting theposition of said brushes with respect to said commutator.

5. An electric conversion system compris-` ing in combination, a sourceof polyphase current of one system, a transformer having very smallleakage-inductance `adapted to change ysaid current into polyphasecurrent of a different system, a commutator, a collecting device andbrushes for successively short-circuiting the secondaries of saidtransformer and thereby converting ysaid polyphase current intopractically-unluctuating direct current, and means for adjusting theposition of said brushes with respect to said commutator. i

6. An electric conversion system comprising in combination, a source ofpolyphasc current of one system, a transformer having very smallleakage-inductance adapted to change saidcurrent to polyphase current ofa different system, a commutator, a plurality of brushes therefor, meansfor creating relative motion between Said commutator and brushes insynchronism with said cul-, rent, a plurality of conductors connectingthe secondaries of said transformer With said brushes, means for takingoff the resulting practically-unfluctuating direct current from saidcommutator, said means com- 'prising apparatus forsimultaneouslyconnecting or disconnecting at a plurality of points in series'thedirect current circuit to or from the secondaries of said transformer,and means for connecting a condenser to each secondary during thecommutation thereof.

7. An electric conversion system comprising in combination, a source ofpolyphase current having a given number ofphases, a transformer havingvery small leakage-inductauce adapted to change said current toe 8. Anelectric coi'iversion system comprising in combination, a source ofdirect current, means for converting the energy of said directI currentinto polyphase energy, a transformer having very small.leakage-iuductance for changing the potential of said polyphase energy,and means associated with the secondaries of said transformer comprisinga collecting device for successively short-circuiting the latter andthereby converting said polyphase energy into practically-unluctuatingdirect current energy having a potential different from that of saidsource.

An electric conversion systemA comprising in combination, a source ofpolyphase current of one system, atransformer adapted to change said.current to polyphase current of a different system, and means connectedwith the secondaries of said transformer comprising a collecting devicefor said polyphasecurrent may be sparklessly commutated for all loadswithin the rated output of said transformer with a fixed angle ofcommutation.

l0. An electric conversion system comprising in combination, a source ofpoly/*phase current having a given number of phases, a transformer forchanging said current into polyphase current having a greater number ofphases, and means connected with the secondaries of said"` transformercomprising a collecting device for successively short-circuiting thelatter and thereby converting said last-mentioned polyphase current intopractically-unfluctuating direct current, said transformer having aleakage-inductance sufficiently small that said polyphuse current may besparklessly commutated for all loads within the rated output of saidtransformer with a lined angle of commutation.

1l. An electric conversion system comprising in combination, a `sourceof polypliase current having a given number of ph: ses, a

transformer adapted to change said current lto polyphase current havinga greater numsparklessly connnutated for all loads within lll@ iso

' the rated output of said transformer with a fined angle ofcommutation. l

12. An electric conversion system comprising in combination, a source ofpolyphase current having a given number of phases, a transformer adaptedto change said current to polyphase current having a greater number ofphases, said transformerhaving a leakage-inductance sufficiently smallthat said polyphase current may be sparlrlessly commutated for all loadswithin the rated output of said transformer With a xed angle ofcommutation, and means for converting said last-mentioned polyphasecurrent into practically-unfluctuating direct current, said meanscomprising means for simultaneously connecting or disconnecting at aplurality of point-s in series the direct current circuit to or from thesecondaries of said transformer.

13. An electric conversion system comprising in combination, a source ofpolyphase current of one system, a transformer adapted to change saidcurrent to polyphase current of a dierent system, said transformerhaving a leakage-inductance suiiiciently small that said polyphasecurrent may be sparklessly commutated for the rated output of saidtransformer with a fixed angle of commutatioma commutator, a pluralityof brushes therefor, means for creating relative motion between saidcommutator and brushes in synchronism With said current, a plurality ofconductors connecting the secondaries of said transformer with saidbrushes, and means fortaking 0E theresulting practically-uniuctuatingdirect-l current from said commutator, said means comprising means forsimultaneously connecting or disconnecting at a plurality of points inseries the direct current circuit to or from the secondaries of saidtransformer.

14. An electric conversion system comprising in combination, a source ofpolyphase current, a transformer, connections from the.'

primaries of said transformer to said source a collecting device 'andbrushes for successively short-circuiting the secondaries of saidtransformer and thereby converting said .polyphase current intopractically-unfluctuating direct current, and means for adjusting thepositionA of said brushes with respect to said commutator,

said transformer having a leakage-inductance sufciently small that saidpolyphase current may be' sparlrlessly commutated for all loadsWithinthe rated output of said ytransformer with a fixed angle ofcommutation.

15. An electric conversion system comprising in combination, a source ofpolyphase current of one system, a transformer adapted to change saidcurrent into polyphase current of a different system, afcoinmutator,

a collecting device and brushes for succesfluctuating direct current,and means for adall loads within- .phases, a transformer adapted tochange said greater rent into practically-unfluctuating direct Ving aleakage-inductance sufficiently small sively short-circuiting theseconda-ries of said transformer and thereby converting said polyphasecurrent into practically-unjusting theposition of said brushes withrespect to said commutator, said transformer having a'leakage-inductance suiiciently small that said polyphase current may besparklessly commutated for all loads Within the rated output of saidtransformer with a xed angle of commutation.

16. An electric conversion system com-A prising in combination, a sourceof polyphase current of one system, a transformeradapted to change saidcurrent to polyphase current of a different system, a commutator, aplurality of brushes therefor, means for creating relative motionbetween said commutator and brushes in synchronism with said current, aplurality of conductors connecting the secondaries of said transformerwith said brushes, and means for taking oil' the resultingpractically-uniiuctuating direct current fi'om said commutator,saidmeans comprising apparatus for simultaneously connecting ordisconnecting at a plurality of points in series the direct currentcircuit to or from the secondaries of said transformer, said transformerhaving a leakage-inductance suiiiciently small that said polyphasecurrent may be sparklessly commutated for all loads Within the ratedoutput of said transformer with a fixed angle of commutation.

17. An electric conversion system comprising in combination, a source ofpolyphase current having a given number of current to polypliase currenthaving a number of phases, means for cnverting said last-mentionedpolypliase curcurrent, said means comprising apparatus forsimultaneously connecting or disconnecting at a. plurality of points inseries the direct current circuit to or from the secondariesv of saidtransformer, and means for con/neet'- ing a condenser to each secondaryduring the commutation thereof, said transformer havthat said polyphasecurrent may be sparklessly commutated for all loads Within the ratedoutput of said transformer with a fixed angle of commutation.

18. An electric conversion system comprising in combination, al sourceof direct current, means for converting the energy of said directcurrent into polyphase energy, a transformer for changing the potentialof said polyphase energy, and means associated with the secondary ofsaid transformer for convertino' said poly/phase energy intopractically-unfluctuating directcurrent energy having a npotentialdifferent from that of said source, said transformer having a leakrentto polyphase current having a greater age-inductance sufficientlyv smallthat said polyphase energy may be sparklessly commutated for alluloadsWithin the rated output of said transformer with a fixed angle ofcommutation.

19. An electric conversion system comprising infcoiifibination, a sourceof poly phase current, means for converting the saine intopractically-unfluctuating direct current, and means for simultaneouslyconiiecting or disconnecting at a plurality of points in series thedirect current circuit to or from said source of polypliase current.

20. An. electric conversion system coinprising in combination, a sourceof ypolyphasc current having a plurality of Windings, means forconimutating said windings to convert said polyphase current intopractically-unluctuating direct current, means for simultaneouslyconnecting or disconnecting at a plurality of points in series thedirect current circuit to or from said source of polypliase current, andmeans for connecting a condenser to cach of said windings during thecommutation thereof. l

2l. An electric conversion system'coniprisiiig in combination, a sourceof polypliase current, a transformer, connections from the primaries ofsaid transformer to said. source, and means connected with thesecondaries of said transformer comprising a collecting device forsuccessively shortcircuiting the latter and thereby converting rsaidpolyphase current into practically-'unfluctuating direct current, saidtransformer having a leakage-inductance suiciently small that saidpolyphase current may be sparklessly comniutated for all loads Withinthe rated output of said transformer With a fixed angle of commutation.4 v 'I 22. An electric conversion system com` prising in combination,` asource of polyc hase current hayinO' a 0'iven number oliv converting thelast-mentioned -polyphase phases, a transformer having very smallleakaGe-iiiductance for changing saidcurt? b b number of phases, saidtransformer having all of its inductivelynssociated primary andsecondary windings y on each core vsand- Wiched or mutually interleavedand evenly distributed throughout the same positionin space, 'and meansi for4 converting the last mentioned polypliase vcurrent intopractically-unfluctuating direct current, said. means comprising meansfor successively shortciiy cuitingthe secondaries ofi-said transformer'and apparatus for simultaneously.connecting or disconnecting at aplurality ofpoints in' series the direct current circuit 'to or fromsaid secondaries.. l l.

QBJAn electric conversion system cornprisingv'in combination, a lsourceofelectrical lenerg ,a transformerl having a yrelatively i smallnumber-of cores,`means causing 'said Venergy to establish av polypliasevmagnetic phases, a transformer for c Y rent to polypliase currenthawinga greater flux in said cores, windings about said cores i'orchanging the potential' of said energy,

said windings constituting a symmetricalv polyphase system connected inpolygon and having a relatively largenumberv of phases, and a commutatorelectrically c ected with said windings for successivelylshortcircuiting the secondaries of said transfornier, said transformer.having allot its-inl ductively-associated primary andsecondaryivindings on each core sandwiched or mii-tw ally interleavedand evenly distributed throughout the saine position in space, whereby asufficiently small lealmgefin',duct-l ance is obtained toallow sparklesscommute:

energy, a transformer haring relatively small number of cores, meanscausing `said energy to establishr a polypliase magnetic-y iiiix in saidcores, windings about said cores for changing the potential -of saidenergy,

said windings constituting symmetrical polypliase system connected inpolygon and having a relativel f large number ,of iliases,

b i. n

and a conimutator electrifaillyl connected with lsaid windings forsuccessively short?.

ciicuiting the secoiidaries of-said transforl lmer; said transformerhayingla sufliciently small co-eiiicient of leakage induction for eachof the last mentionedphasesl to allo'W sparkless commutation ffor. the,full4 rated'- output oi. the transformer with a fixed angleA ofcommutation. i Y l l 25. In an electric-conversion.system, comprising incombination,` a tsource of polyphase ,current having a.Givenjnumber-'off i hanging' said c urniimber of phases, and acoinmutator for current into practical'lyf-nnlu'c'tiiating directcurrent,l said commntator comprising means for `successivelykshort-circiiiting:thesecond.- l'

in the order necessary -for eomniutationz' "ii o current circuit to Vor'from said secondaries 26.An electric conversion system, ccm v prisingin combinatioina source of poly j phase current, means for converting,the

same linto vpractieallyfuiifluctuatingl *direct current and vmeans-for.simultaneously connecting'or disconnecting at 'a :plurality of vpointsinseriesthe direct current lcircuit toA or from said-source of polyphase'current the vorder necessary `for commutation. Y

ings, means for commutatii'ig said windings 27-.liln`electric conversionsystem comvprising in combination, Sa sourcev of pcly- `hase currenthaving a plurality of' windto convert said polyphase current intopractically-unuctuatmg direct current, means for simultaneouslyconnecting or disconnect- 28. An electric conversion system, com-Aprismg m combination, a source of electrical energy, a transformerhaving a relatively small number of cores, a primary winding on saidcores, a secondary winding having a..

relatively large number of integral portions on said cores, eachintegral portion of said secondary winding being distributed in asnearly even a manner as possible throughout the same position in spacesurrounding its core as is occupied by yits inductivelyassociatedprimary winding, whereby the leakage inductance of said transformerreferred to any one of saidintegral portions of said secondary windingisrendered very small, connections between said source of electricalenergyand said primary winding,

a commutator for successively short-circuitving said integral portions`of said secondary winding, and connections between saidsecondary windingand said commutator.

29. An electric conversion system comprising in combination, a source ofelectrical energy, a transformer having a relatively small number ofcores, a primary winding on said core, a secondary winding having arelatively large number of integral portions on said cores, eachintegral portion of said secondary winding being distributed in asnearly even a manner as possible throughout the same position in spacesurrounding its core as is occupied by its inductivelyassociatedprimary-winding, whereby the leakage inductance of said transformerreferred to any one ofsaid integral portions of said secondary windingis rendered suiiiciently small to allow sparkless commutation for allloads within the rated output of the transformer with a xed angle ofcommutation, connections between said source of electrical energy andsaid primary winding, a commutator for successively sliertcircuitingsaid integral port-ions of said secendary winding, and connectionsbetween said secondary winding and said commutator.

30. An electric conversion system comprising in combination, a source ofpolyphase current, a transformer having very small leakage-inductance,connections from the primaries of said transformer to said source andmeans connected with the secondaries of said transformer' comprising acollecting device for successively short-circuting the and therebyconverting said polyphase current into practically-uniuctuating directcurrent.

31. An `electric conversion system comprising in combination, a sourceof polyphase current of one system, a transformer having very smallleakage-inductance adapted to change said current to polyphase currentof a different system, and means comprising a collecting device forsuccessively short-circuiting the secondaries of said transformerandi-thereby converting the last mentioned polyphase current into`practically-unfluctuating direct current.

`32. An electric conversion. system comprising in combination, a sourceof polyphase current having a givennumber of phas, a transformerhavingvery small lealrage-inductance adapted to change said 'current topolyphase current havmg a greater number of phases, and means comprisinga collecting device for successively short-circuiting the secondaries ofsaid transformer and thereby converting said last mentioned polyphasecurrent into practically-unluctuating direct current.

33. Anelectric conversion system comprising in combination, a source ofpolyphaise current, a transformer having very small leakage-inductance,connections from the primaries of said transformer to said source andmeans connected with the secondaries of said transformer comprising acollecting device for successively short-circuiting the latter andreversing the current therein whereby said polyphase current isconverted into practicaily-unfluctuating direct current.

3l. An electric conversion system comprising in combination, a source ofpolyphase current of one system, a transformer having very smallleakage-inductance adapted to change said current to polyphase currentof a different system, and means comprising a collecting device forsuccessively short-circuiting the secondaries of said transformer andreversing the current therein whereby said polyphase current isconverted into practically-unluctuating direct current.

35. An electric conversion system comprising in combination, a source ofpolyphase current having a given number of phases, a transformer havingvery small leakage-inductance adapted to change said current topolyphase current having a greater-number of phases, and meanscomprising a collecting device for successively short-circuiting thesecondaries of said transformer and reversing the current thereinwhereby said polyphase current is converted intopracticallyuniiuctuating direct current.

3G. An electricy conversion system vcomprising in combination a sourceof polyphase electrical energy having a relatively small number ofphases, a transformer having its 4 cores numerically equal to the numberof said phases, a primary Windingfor each of throughout the sameposition in space rounding its core as occupied by the Whole ot itsinductively-associated primary 'windn ing whereby the magnetic fluxlinked with l any one of said intecral portions of said secondaryWinding' is minimized and the reversal of current iny each integralportion of said secondary Winding during.;` commutation for all loads'Within the rated output of the transformer is caused to develop a re-vactance-voltag'e sutliciently small to be sparklessly neutralized by thecomunitation-volt age ivitli a fired angle ol ccunmutatiini.

3i'. An Velectric conversion system coinprisi'ng in combination apolyphase electric circuit having a relatively large number of phases` atransformer having its cores numerically less than the number of saidphases, a prii'nary iinding' for cach of said phases, said windingforminga symmetrical polyphase system connected in polygon, a secondaryWinding for obtainingr a relatively small number of phases, aconnnutating de vice connected to said primary Winding, forsuccessively'l "short-circuiting the integral portionsthereo and adirect current source connected to said commutating device7 eachintegral portion of said 'primary Winding being' distributed in asnearly even a manner as possible throughout the same position in spacesurrounding .its core as is occupied by the whole of itsinductivelyassociated v`secondary Winding, whereby the magnetic l'luXlinlied with any one of said integral "po1'.-

ions of said primary Winding is minimized y i and the reversal ofcurrent in each integral portion of said 'primary winding' during;commutation `for all loads Within the rated output of the transformer iscaused to de-v velop a rcactance-voltage su'fiiciently small tobe'sparkiessly neutralized by the commu-ltatioirvoltage with a fixedangle of comniu-'.

tation. l v H y '88. An electric conversion system comprising incombination a polyphase transformer having closed magnetic circuits anda relatively small number of cores, a pri mary Winding havingitsintegral portions ,numerically larger than the number of said.

cores, said winding forming a symmetrical polyphase system connected vinpolygon, a

commu'tating device connected-tosai'd priH 'eiilolent .ofleakage-induction by' the r y for all loads mary Winding forsuccessively short-circuiting the intevral portions thereof, a lsourceof directfcnrient electrical-energy connected. to said commutatingdevice, a secondary Winding"having its integral portions nun'ierically`equal to those oit the. primary Winding audits turns numericallydifferent :from those of said primary Winding, a second comunitatingdevice connected to said sec ndary wi. ding' for successively shortcircuiting; the integral portions thereof, means -t'or rota-ting bothcomn'iutating devices at the saine speed, and a directlcurrentloa'xd-circuit connected to said second comniutating' device, eachintegral portion of said Secondary Winding being distributed lin nearlyeven a manner as possible throughoiiat the saine position in spacesurrounding its core is occupied by the corresponding'inductivelyassociated portion of said primary Winding whereby magneticillu; linked with corresponddng,` portions of said primary and secondary`windings is minimized and reversal of current .in each phase ofsaidfwindin'gs during coimnuta'tion for all loads Within the ratedoutput of the transm'iner is caused'to develop a reactance-voltagesufficiently small to be sparklessly neutralized by 'the commutationvoltage 'with a fixed angle olf commutation.

An electric conversion system coinprising in combination a. source ofpoly- `phase electrical energy having a relatively being Aso disposed.about its corefand* so in-v ductively interlinked with its associatedpriinl "winding.mat the productor' 'its co4-v n vate of current change'during the pt niod ot current reversal in' such-integral portion iseoualto la'reactance voltage -suiicientlysmall to be spairlrlesslynenti'. iced' by lthe commutation 4voltage with a fixed angle'ofcommutation 'itliin the rated output of the transformer.- j y flin@electric comiersionv system cona-A prising in combination a source ofpolyphase current :f having. ,given viluminar of phases, atranslormerfor changing said current' into polyphase current having a; greaternumber of phases, Iconnections from the primary of said transformer tosaid source and a commutator for successively short-creuit- In testimonywhereof, I have hereunto lng the secondames of sind transformer andsubscrlbed my name thls 16 day of Aug., reversmg the current thereln,Saud trans- 1912.

former having such small leakage-nduct- SEVVALL CABOT. 5' ance that thereaetance-yoltuge developed by Witnesses:

such current reversal is substantially' equal PATRICK J. CONROY,

to the commutation-voltage. GEO. K. WooDwoRTH.

cupio: o! this patent my be obtxined for nve oentl uch, by uldxening theConliuioner of hunts. Washington, D. G.

